f008738abd
Dart type inference does not propagate type sideways in the argument lists[1], so we have to explicitly provide fold with a type argument, otherwise it is inferred as `Object?`, which does not work in this case. [1] https://github.com/dart-lang/language/issues/731 Change-Id: I2ee0bda2cd6c37c64018efd48ea14c469f76ba3a Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152003 Reviewed-by: Martin Kustermann <kustermann@google.com> Commit-Queue: Vyacheslav Egorov <vegorov@google.com>